Many small marine vessels, such as fishing boats, have manual hydraulic rather than power steering. Such vessels are controlled by rotating a steering wheel which causes delivery of hydraulic fluid from a helm pump directly to one or more steering cylinders which control the position of the vessel's rudder. The disadvantages of manual steering are well recognized. For example, the steering wheel must typically be rotated a large number of revolutions in order to change the direction of the vessel. Generally speaking, the larger the vessel, the more effort is required to steer manually.
Other steering problems may arise in large marine vessels such as tankers (which typically include power steering systems). The primary problem is that it is not possible to effectively steer such vessels from the wheelhouse if the power system fails. Rather, the pilot must instruct remote operators in the steering gear flat or compartment to manually alter the position of the steering cylinders. If this back-up voice communication system fails, or if the pilot's instructions are misunderstood or misinterpreted, safe control of the vessel may be lost.
It is known in the prior art to provide manual emergency steering in the event of power steering failure, but such systems are often unreliable or expensive to install. U.S. Pat. No. 3,468,126, which Was granted to Mercier on Sept. 23, 1969, discloses a hydraulic position control system for controlling the direction of a ship which includes manual or electrical control means. In the event of a power failure, a manually operated hydraulic fluid pump is connected directly to the steering cylinders to permit manual operation of the vessel. The primary disadvantage of the Mercier system is that it is relatively complicated and expensive to manufacture and it cannot be easily retrofitted into existing vessels, such as small-sized fishing boats. Further, the Mercier system does not specifically disclose any means for converting a manual hydraulic steering signal into a proportional electrical signal.
The need has arisen for a steering signal conversion apparatus which can be conveniently retrofitted into existing vessels to provide power steering, and which may also be readily installed in larger vessels to provide back-up, emergency manual steering. The present invention satisfies both these needs in a simple and economical manner.